Linear motion is known in the art and is achieved in numerous ways. Vertical, linear motion is also known and, in particular, is utilized in automatic opening and closing of car windows.
There are many types of mechanisms to open and close a car window, one of which is shown in FIG. 1 to which reference is made. The structure includes at least a base 10 for the window 12 and four criss-crossed rods 14 attached to each other at pivots 16. Two of the rods 14 (those labeled 14a and 14b ) are attached to the base 10 also by pivots 16. Rod 14c is rotatably attached to a movable rack 18 while rod 14d is rotatably attached to a stationary rack 19; both racks are moved by a rotatable pinion 20. Pinion 20 can be operated manually or via a motor (not shown).
When pinion 20 rotates, it causes rack 18 to move to the right or left, as indicated by arrow 22. When rack 18 moves to the left, it pulls rod 14c to the left, which causes rod 14d to pivot counterclockwise. In response to the lowering movement of both rods 14c and 14d, rods 14a and 14b become more horizontal and thus, the window 12 is lowered. The opposite occurs when the rack 18 is moved to the right.
The structure shown in FIG. 1 is extremely bulky, requiring the entire inner space of a door. Furthermore, operation of the structure creates a large dynamic force which cannot quickly be stopped. Thus, an arm can easily be caught and tightly pressed between the window and its outer window frame (not shown in FIG. 1).
Piezoelectric motors are known in the art. SU 693493 describes a piezoelectric motor comprising a flat rectangular piezoelectric plate having one electrode covering essentially all of one large face of the plate ("the back face") and four electrodes each covering a quadrant of the front face. The back electrode is grounded and the electrodes of the front face are electrically connected on the diagonal. Two ceramic pads are attached to one of the long edges of the plate and these pads are pressed against the object to be moved by a spring mechanism which presses the other long edge.
The long and short edges of the piezoelectric ceramic have similar resonant frequencies (for different mode orders) such that, when one pair of connected electrodes is excited with an alternating current (AC) voltage to which the ceramic is responsive, the object moves in one direction, and when the other pair of electrodes is excited, the object moves in the other direction.